In a work environment, the accumulated amount of noise, or dose in terms of an average noise level, and the maximum level of noise to which an individual has been exposed during a workday are important to occupational safety and to the health of the individual. Industry and governmental agencies in countries throughout the world, such as the Occupational Safety and Health Administration (OSHA) in the United States, require accurate sound data measurements.
Examples of such sound data measurements include impulse noise, continuous noise, and an eight-hour time-weighted average (“TWA”) that is also referred to as “daily personal noise exposure”. Impulse noise relates to noise of very short duration. Continuous noise relates to noise that is longer in duration than impact noise, extending longer than 500 milliseconds. Eight-hour TWA relates to the average of all levels of impulse and continuous noise to which an employee is exposed during an eight-hour workday. The OSHA maximum level for impulse noise is 140 dBSPL measured with a fast peak-hold sound level meter (“dBSPL” stands for sound pressure level, or a magnitude of pressure disturbance in air, measured in decibels, a logarithmic scale). The maximum level for continuous noise is 115 dB(A) (read on the slow average with A-weighting). OSHA regulations limit an eight-hour TWA to 90 dB(A). If employees are exposed to eight-hour TWAs between 85 and 90 dB(A), OSHA requires employers to initiate a hearing conservation program which includes annual hearing tests.
Sound exposure (which includes both undesirable noise and personal entertainment or other desired sound) requirements in many countries are becoming more and more stringent and in particular, headsets used for personal entertainment (music, gaming and other multimedia) are being required to limit the daily sound exposure to a specific dB level. It is expected that these dB limits will be reduced in future legislation. It has been found that typical headset or headphone users tend to listen to lower level at the beginning, after a period of time, they like to increase the loudness gradually to maintain the excitement and energy level of the multimedia program they are enjoying.
Current sound exposure limiting solutions in headset measure the sound pressure level being delivered over a short period of time (e.g. 10 mins) and then assume that the level will be maintained for the entire listening session (2, 4, 8 hour period) and limit the loudness accordingly. This approach is simple to implement but fails to account for the fact that a user may have been listening below the limit for a period of time prior to and/or after turning up the volume. This means that the user can never listen above the average sound pressure limit even though it would be safe to do so as their daily exposure dose is well below the regulated limit. Many users find this simple limiting frustrating and a detriment to their listening experience. As a result, improved methods and apparatuses for limiting sound exposure are needed.